Sets the CSS file used for the message tab for the network <network>. <motif> can be a URL to a .css file, or the shortcut "dark" or "light". If <motif> is a minus ('-') character, the motif will revert to the global motif. If <network> is not provided, the current network is assumed. See the ChatZilla homepage at <http://www.mozilla.org/projects/rt-messaging/chatzilla/> for more information on how to style ChatZilla. See also |motif|.